The present invention relates to a mine roof support in which a roof shield, pressed by hydraulically operated collapsable and extensible props arranged between the roof shield and a sole plate, against the roof of a mine gallery, is connected at its rear end to a rear shield, which in turn is connected by links to the rear end of the sole plate, and in which a hydraulically operated cylinder-and-piston unit is interconnected between the roof shield and the rear shield for controlling the included angle between the same.
Such mine roof supports are known in the art. In the end positions of the roof shield, that is in which the roof shield includes a maximum or a minimum angle with the rear shield, mechanical stops are provided in this known mine roof support for these end positions of the roof shield relative to the rear shield and such mechanical stops may be provided in the aforementioned cylinder-and-piston unit interconnected between the shields. In order to avoid in such a case damage of the mine roof support resulting from the tremendous forces transmitted from the props over the linkage onto the aforementioned stops, there have up to now been provided shear bolts as overload safety means, which in the event of an overload have been sheared off.
During operation of such mine roof supports in mine galleries of low height, the end stops will soon be engaged. If under such condition the shear bolt is sheared off, a new shear bolt has to be provided in its place to assure further safety against overload, which evidently reduces the efficiency of this known mine roof support.